Check the clutch free play as it might be rotating the input shaft more then it likes. Also I noticed you said fresh oil but did not reference what grade and type . Yours being a 05 should be 15w50 4rt mobile one. If not that then I would recommend a oil close to the same like ams oil 20w0 or Motul 300 V 15w50 or even redline 20w50 People have noticed a difference when running thing like castrol.
anyway that and proper free play would be my first recommendation
If there is a lot of new gears it might need some break in thrashing!!!!!!!!!!!!!!!!!!